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Part I: An introduction to basic nuclear science. Why study nuclei Basic facts about Nuclei Nuclear structure and nuclear reactions Basic facts about collisions and reactions Where we do our experiments How we do the experiments What one can learn from debris.

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slide1

Part I: An introduction to basic nuclear science

Why study nuclei

Basic facts about Nuclei

Nuclear structure and nuclear reactions

Basic facts about collisions and reactions

Where we do our experiments

How we do the experiments

What one can learn from debris

Nuclear Chemistry at Indiana: http://nuchem.iucf.indiana.edu

Romualdo T. de Souza

slide2

1) Why study nuclei?

  • Nuclei are at the heart of every atom; What is their structure, properties? What is the nature of the force that hold them together?
  • Necessary to understand the formation of the elements – nucleosynthesis
  • Important in understanding the properties of astrophysical objects such as neutron stars ( a giant nucleus with a radius of ~ 0.6 km)  nuclear equation-of-state.
  • Important in understanding the thermodynamic properties of small, finite systems (ties to the study of atomic clusters).
  • Important in understanding nuclear fission and nuclear fusion (energy source/ weapons)

Stable Nuclei

Known Nuclei

Terra Incognita

Protons

Neutrons

Romualdo de Souza

slide3

1) Why study nuclei?

Only elements Z=1-4 produced in the Big Bang

 Fundamentals of supernova explosions are not understood!

 Synthesis of the heavy elements is not understood

 Limits of nuclear stability (superheavy elements, N/Z exotic) poorly known

slide4

2) Basic facts about nuclei:

  • Nuclei behave like microscopic drops of liquid (fairly incompressible yet deformable).
  • Nuclei are small (R= 1-10 x 10-15 m);104-105 times smaller than an atom; requires measuring instruments of a comparable size to measure them e.g. other nuclei
  • Nuclei are positively charged so one has to overcome the mutual repulsion between two nuclei (Coulomb repulsion) i.e. Particle accelerators are required.
slide5

2) Basic facts about nuclei: Binding energy

TBE= Total Binding Energy

Analogous to the heat of vaporization

TBE/A = “average bond strength”

Binding energy curve for nuclei

How can one understand this binding energy curve?

slide6

2) Basic facts about nuclei: The liquid drop model

Charge denisty, 

Radial distance (r)

TBE = C1A C2A2/3 C3Z2/A1/3 C4(N-Z)2/A2 + C6/A1/2

volume

surface

Coulomb

symmetry

pairing

<BE> = TBE/A

<BE> = C1 C2A1/3 C3Z2/A4/3 C4(N-Z)2/A3+ C6/A3/2

slide7

2) Basic facts about nuclei: The liquid drop model

The first three terms in the liquid drop model (Volume, surface, and Coulomb) already explain the shape and magnitude of the Binding energy curve for nuclei.

slide8

2) Basic facts about nuclei: The shell model

Nuclei are not “formless blobs”. They have an internal structure in which protons and neutrons occupy orbitals much as in the atom (though with differences).

Proton number Z

(Mmeasured – Mliquid drop)c2

Neutron number N

Red arrows indicate nuclei of additional stability. They occur at the MAGIC NUMBERS: 2,8,20,50,82, and 126

slide9

3) Nuclear structure and nuclear reactions

Nuclear structure involves studying the internal levels in a nucleus. Since the transition between levels involves the emission of gamma rays, nuclear structure involves gamma ray spectroscopy

110 Ge detectors on a 10 inch radius sphere

The next generation: Segmented Gamma ray detectors (GRETINA)

slide10

3) Nuclear structure and nuclear reactions

  • total number of protons is conserved
  • total number of neutrons is conserved
  • Q (energy release) can be either positive (exothermic) or negative (endothermic)
  • to get the nuclei to react one must get into the range of the short range nuclear force (projectile and target nuclei must touch)
  • The reaction products are quite likely excited (their protons and neutrons are not in the ground state) and they will de-excite by emission of gamma rays, neutrons, protons, alpha particles and other clusters.
slide11

4) Basic facts about collisions and reactions?

camera

Classical drops: Collisions of mercury drops

Deposit of a fraction of initial kinetic energy into heat and stretching the drops. How strong is the inter-atomic interaction? Role of surface tension.

We want to study the same type of processes but with nuclear drops to learn about the forces holding nuclei together!

Impact parameter selection: direct inspection

t=0 ms

30 ms

60 ms

90 ms

120 ms

150 ms

Fusion-like event

Strongly Damped/Deeply inelastic event

Deep inelastic + neck emissions event

slide12

Antisymmetrized Molecular Dynamics

Supercomputer simulations of 114Cd + 92Mo at E/A = 50 MeV; b=7.37 fm

iu cyclotron facility

http://www.iucf.indiana.edu

IU Cyclotron Facility

The Indiana University Cyclotron Facility (IUCF) is a multidisciplinary laboratory performing research and development in the areas of accelerator physics, nuclear physics, materials science, life science and biomedical applications of accelerators.

Accelerator PhysicsDefining the physics of producing and handling beams of sub-atomic particles

Biomedical and Life SciencesHarnessing the power of radiation for research in biology and medicine

Materials ResearchImaging, modeling and manipulating macromolecules

Neutron PhysicsUsing neutrons to explore the molecular structure of proteins, crystals, surfaces, and much more

Nuclear Physics and ChemistryProbing matter and forces at the sub-atomic scale

slide15

5) Where we do our experiments (the accelerator side )

Ion sources

  • Up to C at 96MeV/A or U at 24MeV/A
  • CSS1, CSS2 K=380
  • SISSI - fragmentation beams
  • SPIRAL - re-acceleration of radioactive beams with CIME
slide16

Principle of acceleration of a cyclotron

  • 4 dipole magnets act to bend the moving charged particle in a circular orbit
  • a voltage applied at radiofrequency as the particle moves between the dipoles causes the particle to accelerate, therefore spiraling outward
  • When the particle reaches the maximum radius of the cyclotron it is at the maximum energy and is extracted by a small electrostatic deflection
slide17

A sense of scale : A K=200 cyclotron (IUCF)

  • Remember that GANIL has two K=380 cyclotrons coupled sequentially
  • Michigan State has two coupled superconducting cyclotrons (K=500 and K=1200)
slide18

6) How we do our experiments (the detector side)

Interaction of radiation with matter!

Charged particles: protons, deuterons, tritons, alpha particles, intermediate mass fragments (IMF: 3≤Z≤20), fission fragments

Gas detectors (incident particles cause ionization)

Solid state detectors: Si, Ge (incident particles cause electron-hole pairs)

  • Neutral particles:
  • gamma rays
  • neutrons

Scintillators: liquid, plastic (incident particles cause scintillation)

slide19

6) How we do our experiments (the detector side)

E detector

dE  Z2A

Incident particle with (Z,A,E)

dx

E

dx

Interaction of radiation with matter!

E detector

Different “bands” represent different isotopes.

slide20

6) How we do our experiments (the detector side)

Backed by CsI(Tl) with photodiode readout …

Are stacked to make a telescope…

Segmented Si detectors

4x CsI(Tl) 4cm

Si-E 1.5 mm

Si-DE 65mm

pixel

16 strips v (front)

16 strips h. (back)

Target

16 strips v. (front)

Beam

And electronics…

slide21

6) How we do our experiments (the detector side)

Many telescopes are combined together to give as complete a measurement as possible.

slide22

7) What one can learn from debris

Collision of a nucleus with a light-ion (Z<3) or a heavy-ion (Z>2) converts kinetic energy of relative motion into intrinsic excitation i.e. heats the nucleus.

From the debris – the fragmentation pattern we need to determine what happened

  • identity of all the particles
  • number of clusters (Z>2)
  • number of light particles Z=1,2
  • energy of all the particles
  • angles of all the particles
slide23

4 measurements

ISiS: Indiana Silicion Sphere

We measure all information collision-by-collision (event-by-event).

  • 162 individual telescopes covering 74% of 4
  • Gas Ionization chamber/500 µm Si(IP)/CsI(Tl(PD)
  • Each telescope measures Z,A, E, and 
  • Identification of Z for 0.6≤E/A≤96 MeV
  • Identification of A for E/A ≥ 8 MeV for Z≤4
thermometers
Thermometers

Kinetic equilibrium: motion of all particles reflects a common temperature

H2 gas

P(v)

v (m/s)

Physical Chemistry, R. Chang, 2000

  • Maxwell Boltzmann distribution
  • Coulomb Barrier for α-particles

Helium Isotopes

Kinetic energy spectra fit

 Maxwell-Boltzman distribution

 TSlope

Charity, et.al., PRC (2001)

slide25

Angular distribution: comparing emission time to rotation time

When the rotation time is short compared to the emission time, a uniform emission pattern is observed.

Emission from a hot nucleus

Circular ridge  PLF* emission

“Isotropic” component

Other emission

(mid-rapidity, ...)

Projectile velocity

slide26

Another Thermometer: Excited state populations

Chemical equilibrium: different partitions are populated according to their statistical weights.

Relative energy spectrum of daughters reflects internal quantum levels of parent

6Li

Emitting system

F. Zhu et al., PRC52, 784 (1995)

10B

Pm = (2Jm+1)e-(E*-Em/T)

Pm/Pn = (2Jm+1)/(2Jn+1)e-(En-Em)/T

Extract temperature T

phase transitions for small finite open systems
Phase transitions for small, finite, open systems

Constant P

Infinite matter

Closed system

 Transition from one phase to an other at constant T

“Caloric curve” for nuclear matter

J. Pochodzalla et al., PRL 75, 1040 (1995)

Gas phase

Liquid phase

Liquid-gas coexistenceBOILING ?